1. Field of the Invention
The present invention relates to an automatic gain control apparatus, and more particularly to an automatic gain control apparatus for controlling the magnitude of a reception signal for use in wired/wireless communication such that it can optimally control a plurality of devices contained in a receiver.
2. Description of the Related Art
Typically, an automatic gain controller (AGC) for use in wired/wireless communication guarantees stable operations of a variety of devices contained in a reception end, for example, a timing recovery device, a carrier recovery device, and an equalizer, etc., and maintains the magnitude of a reception signal at a desired level, resulting in reduction of overall performance of a receiver. The magnitude of input signals of the reception end for use in general wired/wireless communication varies with transmission and channel conditions. In this case, provided that the magnitude of input signals is contained in a prescribed dynamic range during which a plurality of blocks contained in the receiver can be operated, overall performances of the receiver may be unexpectedly damaged. Therefore, the automatic gain controller has been adapted to solve the aforementioned problems.
FIG. 1 is a block diagram illustrating a conventional automatic gain control device. Referring to FIG. 1, the conventional automatic gain control device includes an analog signal processor (also called an analog front end block) 110 for processing consecutive analog signals in association with a reception signal S20, and an automatic gain controller 120 for controlling a gain of the analog processor 110. The analog signal processor 110 includes a first analog signal processor 111 for performing a variety of operations, e.g., amplification, BPF (Band Pass Filtering), and frequency conversion operations, etc.; a variable gain amplifier 112 for amplifying the input signal S20 at an amplification rate having been controlled by the gain-controlled voltage calculated by the automatic gain controller 120; and a second analog signal processor 113 for performing a variety of operations on the amplified signal received from the variable gain amplifier 112, for example, LPF (Low Pass Filtering) and ADC (Analog-to-Digital Conversion) operations, etc. The automatic gain controller 120 includes a level detector 121 for detecting a level of an output signal S 21 of the analog signal processor 110; an LPF (Low Pass Filter) 122 for performing an LPF operation on an output signal of the level detector 121; a subtracter 123 for calculating a difference between an output voltage and a reference voltage of the LPF 122 to generate an error signal; and a multiplier 124 for multiplying a loop gain coefficient by an error signal, and applying the multiplied result to a gain control voltage.
The level detector 121 can be configured in the form of a full-wave rectifier. The level detector 121 squares the output signal S21 so that the output signal of the level detector 121 is equal to a power signal of the signal S21. The LPF 122 has an output signal indicative of an integral signal associated with the power signal. In more detail, the output signal of the LPF 122 is indicative of a mean magnitude of the signal S21. Therefore, the subtracter 123 generates a difference (i.e., an error signal) between a true gain of the output signal S21 of the analog signal processor 110 and a target reference gain (i.e., a reference voltage). The multiplier 124 multiplies a loop gain coefficient (also called a loop gain constant) by the error signal, and thereby generates a gain control signal S22 of the variable gain amplifier 112.
A time response characteristic of the aforementioned conventional automatic gain control device is determined by a bandwidth of the LPF 122. In more detail, the narrower the bandwidth of the LPF 122, the longer the time response characteristic. The wider the bandwidth of the LPF 122, the shorter the time response characteristic.
However, current high-speed data communication has been established using burst signals. The burst signal requires a short time interval, such that a reception end requires a high-speed gain control operation to perform normal data recovery. If the aforementioned automatic gain control device is contained in a reception end, the bandwidth of the LPF 122 must be increased. However, provided that the bandwidth of the LPF 122 is excessively increased, a noise component unexpectedly occurs, such that a correct magnitude of the output signal S21 cannot be detected, resulting in the creation of an error associated with the gain control signal S22.
Due to the above-described problems, the conventional automatic gain control device has a limitation in increasing the LPF's bandwidth to establish the above high-speed gain control operation, such that it is difficult to acquire a sufficiently-high gain control speed requested by a high-speed data communication system employing burst signals.
Furthermore, the conventional automatic gain control device has been adapted to process analog signals, resulting in a complicated gain control process and a greater error rate.